DSL technologies provide a cost-effective broadband access solution by reusing the existing infrastructure of POTS (Plain Old Telephone Service) networks. Thus, DSL technologies have come to dominate the broadband access market.
FIG. 1a is a schematic view of a basic DSL system comprising N lines. A line is typically a twisted pair of copper wires. At the DSLAM (Digital Subscriber Line Access Multiplexer) side, a transceiver node 102 is connected to a respective first end of the N lines. The respective other end of the lines is typically connected to a so-called CPE or similar communication equipment.
The performance of DSL systems is limited by line attenuation and crosstalk. In FIG. 1b, FEXT (Far End cross-Talk) is illustrated as a dashed line from one line to another line. Basically, the reach (e.g. in meters) is mainly limited by line attenuation, while the capacity (e.g. in bits/s) is mainly limited by crosstalk from neighboring lines.
The work on further improving the performance of DSL systems is constantly in progress. For example, the use of the recently approved vectoring recommendation, ITU-T G.993.5, enables that crosstalk between DSL lines can be efficiently canceled, which may entail a significant improvement of DSL line capacity.
A new standardization work, ITU-T “G.fast”, has been started in order to enable DSL service from a last distribution point which is located as far as 200 meters away from a user. Within the work on G.fast it is considered to use frequencies of up to 300 MHz, which is higher than for example in current VDSL2 (Very-high-bitrate DSL) systems, where only frequencies of up to 30 MHz are used.